1. Field of the Invention
The present invention relates to a polymerization method of polyisocyanates endcapped with acyl chlorides, and more particularly to a process for preparing polyisocyanate with higher stability comprising endcapping a living polymer chain amidate anion with an acyl chloride derivative in the presence of an amine catalyst, thereby maximizing endcapping ratios.
2. Description of the Related Art
Polyisocyanates are polymers having rigid bonding due to their partial double bonds of amide linkages in the main backbone. In addition, polyisocyanates adopt a helical conformation in a solution as well as in a crystalline state due to their steric hindrance. Their left-handed helices and right-handed helices are homogeneously arranged and therefore provide a similar conformation to biomacromolecules with helical conformation such as nucleic acids and proteins, while polyisocyanates have racemic properties. Asymmetric carbons are introduced into side chains of polyisocyanates to render helical conformation to be in one screw sense for inducing optical activity according to the rule of sergeant and soldier(Akio Teramoto, Macromolecules 1998, 31, 6362–6368), and such helically chiral polyisocyanates are highlighted in view of their application. However, polyisocyanates generally exhibit low ceiling temperature and are susceptible to depolymerization due to their terminal NH group, which decreases the applicability of polyisocyanate to the industrial field. In this regard, for enhancing stability, Drs. Novak and Hatada have reported a method for stabilizing polyisocyanates by coordination polymerization using acetic anhydride derivatives and acetic chloride derivatives as endcapping materials (Patten, T. E.; Novak, B. M. J. Am. Chem. Soc. 1996, 118, 1906, Ute, K.; Hatada, K. Polym. J. 1995, 27, 445). Moreover, Dr. Masaru has suggested a method for endcapping by use of methacryloyl chloride having functionalities for coupling reaction with the end of living anion chain (Kazunori Se, Masaru, D. Macromolecules 2003, 36, 5878). However, the endcapping efficiency was 10–77% due to lower reactivity of living polymer chain amidate anion and thus a complete level of stability was not achieved because complete endcapping was not possible. Accordingly, there still remains a need for developing a novel approach to endcap polyisocyanate having higher efficiency as well as to increase stability and impose characteristics for functional materials.